The present invention relates in general to electronic circuits and, more particularly, to high-speed break-before-make electronic switches.
Electronic switching circuits are used in a myriad of applications to switch analog and digital signals. The electronic switch makes and breaks continuity between electrical nodes. Many switches, commonly known as break-before-make (BBM), are designed to break the old connection before making a new connection to avoid short circuits and potential damage to connecting circuitry. For example, a BBM switch may connect either circuit A to circuit C or circuit B to circuit C. The connection between circuit A and circuit C is broken before the connection between circuit B and circuit C is made. The BBM switch avoids any transient and undesired connection between circuit A and circuit B.
In cellular phone applications, analog switches are used to switch between normal operating mode and sleep mode. In normal operating mode, a fixed frequency oscillator operating at say 4 MHz controls the transmitter and receiver (transceiver) in the cell phone. In sleep mode, a second fixed frequency oscillator operating at 32 KHz allows the transceiver to consume less power. The analog switch connects either the 4 MHz oscillator or the 32 KHz oscillator to the transceiver. It is not desirable at any point in time to have the 4 MHz oscillator and 32 KHz oscillator connected to the transceiver, or to each other, simultaneously. The BBM analog switch prevents such an occurrence. In a similar manner, analog switches can also switch between two different signal types, such as CDMA and TDMA.
In the prior art, the BBM electronic switch uses an RC circuit to impose a time delay between breaking one connection and making another connection. The time delay is set to worse case to insure that the old connection is indeed broken before the new connection is made. Unfortunately, worse case time delays limit the maximum operating switching speed of the analog switch. Moreover, RC delay circuits consume excessive area in integrated circuits.
Hence there is a need for a high-speed BBM switch circuit that increases operating speed, decreases die area, and minimizes costs.